Humalog vs Novolog: Clinical Differences
Humalog (insulin lispro) and Novolog (insulin aspart) are clinically interchangeable rapid-acting insulin analogs with nearly identical pharmacokinetic and pharmacodynamic profiles, though they are not FDA-approved as interchangeable products and require a prescription change to switch between them. 1
Pharmacokinetic Profile
Both insulins have essentially the same time-action characteristics:
- Onset of action: 0.25-0.5 hours (15-30 minutes) 1, 2
- Peak action: 1-3 hours 1, 2
- Duration of action: 3-5 hours 1, 2
The molecular difference is minimal—insulin aspart has proline substituted with aspartic acid at position B28, while insulin lispro has the lysine and proline residues at positions B28 and B29 reversed. 3 Despite these distinct amino acid modifications, their clinical action profiles are nearly identical. 1, 2
Clinical Use and Equivalence
The American Diabetes Association recommends both insulin lispro and insulin aspart as appropriate rapid-acting insulin analogs for prandial insulin in basal-bolus regimens and continuous subcutaneous insulin infusion (insulin pumps) for both type 1 and type 2 diabetes. 1
Both insulins:
- Provide better postprandial glucose control than regular human insulin 2
- Reduce nocturnal and severe hypoglycemia compared to regular insulin, particularly in type 1 diabetes 2
- Can be administered 0-5 minutes before meals 4
- Have similar stability profiles when used in insulin pumps 1
Practical Considerations
When converting between these products, they can be dosed unit-for-unit since their pharmacodynamics are clinically equivalent. 1, 4 However, a prescription change is required because they are not designated as interchangeable products by regulatory authorities. 1
The primary practical difference is cost, which may vary between the two products and could affect patient access and adherence. 1 When one product is unavailable (such as in shortage situations), the other serves as an appropriate substitute using the same dosing strategy. 4
Common Pitfall
Do not assume these products can be automatically substituted at the pharmacy level without a new prescription—despite their clinical equivalence, they require prescriber authorization to switch. 1